THE ROCK IGUANA, CYCLURA PINGUIS,
ON ANEGADA, BRITISH VIRGIN ISLANDS,
WITH NOTES ON CYCLURA RICORDI AND CYCLURA CORNUTA
ON HISPANIOLA

W. MICHAEL CAREY

UNIVERSITY OF FLORIDA

GAINESVILLE

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THE ROCK IGUANA, CYCLURA PINGUIS,

ON ANEGADA, BRITISH VIRGIN ISLANDS,

WITH NOTES ON CYCLURA RICORDI AND CYCLURA CORNUTA

ON HISPANIOLA

W. MICHAEL CAREY1

SYNOPSIS: A field study of the ethoecology of the rock iguana, Cyclura pinguis,
on Anegada, British Virgin Islands was conducted from 27 March to 5 May 1968.
The sympatric Hispaniolan species, C. ricordi and C. cornuta, were observed from
12 to 16 May 1968. The results of these studies and all known ethoecological
literature on the genus are discussed.

Cyclura pinguis inhabits primarily xeric limestone areas, is heliothermic, and
exhibits behavioral thermoregulation. Retreats nearly always consist of natural
cavities in the limestone or beneath boulders. C. ricordi and C. cornuta are primarily
burrowers. Adult of all three species are principally herbivorous, although some
animal matter is taken. Probably all Cyclura juveniles are primarily insectivorous.
Parasitism from ticks and nematodes is a common occurrence in Cyclura. Five adult
males on the main study plot ranged from 522 to 545 mm (v=534.60+3.88 mm)
in snout-vent length and from 5.95 to 7.17 kg (= 6.72+0.21 kg) in body weight;
five adult females ranged from 426 to 487 mm (= 468.00 + 10.87 mm) in snout-
vent length and from 4.31 to 5.13 kg (Y=4.75-0.13 kg) in body weight. The
five males occupied home ranges from 116.06 to 985.11 m2 (Y=546.61-+ 160.46
m') in area; home ranges of the five females measured from 155.47 to 412.31 m2
(T=276.28+41.62 m2). Extensive unutilized zones existed between home ranges
of iguanas of the same sex. Aside from food, available shelter seems to be the
most important factor governing selection of home range locale. Cyclura pinguis
exhibited a density of 2.03 iguanas/hectare (0.82/acre), the lowest density figure

1The author is currently engaged in free-lance writing. The paper was submitted to the Uni-
versity of South Florida, Tampa, in partial fulfillment for the degree of Master of Arts. Manu-
script accepted 10 July 1972.

of any lizard for which data are documented. The sex ratio was equal. Evidence
suggests monogamy. Three adult females had 12, 14, and 16 yolked ovarian follicles.
Adulthood appears to be attained between 7 and 9 years of age and between 350
and 400 mm snout-vent length. The reproductive cycle in C. pinguis suggests
synchronization with the two rainfall maxima in the Virgin Islands. Adult iguanas
far outnumbered juveniles (87.5% vs. 12.5% ) suggesting decline of the population.
This disproportionate age structure seems to be the result of interactions (competi-
tion/predation) with domestic livestock. With the resultant loss in fecundity,
relatively few adults now exist to continue the population. A conservation program
is outlined whereby the population might be restored. This program might be
applicable to other decimated Cyclura populations as well.

INTRODUCTION
Rock, or ground, iguanas (genus Cyclura Harlan) are large, primarily
herbivorous lizards endemic to the Bahamas, Greater Antilles, Cayman
Islands, and Virgin Islands. The current distribution of extant species
is spotty, but Pleistocene and Recent fossil remains have been found on
several islands no longer supporting populations: e.g., St. Thomas (Miller
1918), Puerto Rico (Barbour 1919), Great Exuma (Allen 1937), New
Providence (Etheridge 1966), Navassa (Patton 1967), and possibly Bar-
buda (Etheridge 1964). These remains clarify several distributional pat-
terns.
Only Hispaniola supports sympatric forms. Cyclura ricordi and the
rhinoceros iguana, C. cornuta, occur in portions of the Cul-de-Sac-Valle
de Neiba plains of the Dominican Republic and in scattered areas farther
south on the Barahona Peninsula. These are xeric salt plains that were
once part of a Pleistocene waterway separating the then north and south
islands (sensu Williams 1961) of Hispaniola. This apparently comprises
the total range of C. ricordi, whereas C. cornuta ranges over much of
Hispaniola and several of its satellite islands.

CAREY: CYCLURA PINGUIS

Cyclura belongs in the iguanine line of the family Iguanidae (Savage
1958, Avery and Tanner 1971), but intrageneric relationships are poorly
understood. Hence nomenclature in this paper essentially follows that of
the last systematic treatment of the group (Barbour and Noble 1916) and
subsequent species descriptions. A study of the evolutionary relation-
ships among the species is in progress (Schwartz and Carey, in prepara-
tion).
No previous detailed studies on the ecology and behavior of any
Cyclura species have been done, though several short papers describe
various aspects of their activity. Gosse (1848) first reported habits of
the Jamaican C. lophoma ( =C. collei). Nearly a century later Grant
(1940a) and Lewis (1944, 1946) noted the apparent impending extinc-
tion of this species on Jamaica and Goat Island. Short works on C.
cornuta (Noble 1923, Klingel 1929) and reports dealing with the Ba-
hamian forms C. rileyi (Stejneger 1903), C. figginsi (Bailey 1925), and
C. carinata bartschi and C. nuchalis (Cochran 1934) also have appeared.
Activity of the Cuban C. macleayi macleayi has been reported by Buide
(1951), Street (1952), Sutcliffe (1952), Hardy (1956), and Cooper
(1958). The forms on Cayman Brac and Little Cayman (C. macleayi
caymanensis) and Grand Cayman (C. macleayi lewisi) were studied by
Grant (1940b) and Carey (1966). Grant (1944) also studied C. stejne-
geri on Isla Mona, off the western coast of Puerto Rico.
In addition to the Cyclura species already extinct (mattea, nigerrima,
portoricensis, and a few unnamed forms), several others may face similar
fates, because they inhabit tiny islands and cays-a situation that keeps
many populations, although dense, precariously small. On the Greater
Antilles, where ecological diversity is greater, Cyclura occurs only in
restricted xeric habitats, and their decline or extinction has been caused
primarily by man's activities. Because of the generally precarious status
of Cyclura species, all are listed in the International Union for the Con-
servation of Nature and Natural Resources (IUCN) RED DATA BOOK
on endangered amphibians and reptiles (Honegger 1968).
The present report and that by Carey (1966) are parts of a projected
series of studies concerning the ecology and behavior of West Indian rock
iguanas. The results will provide means for interpreting ethoecological
components of the generalized Cyclura niche in these discrete but
roughly similar insular communities.
This report on the ethoecology of the rock iguana, Cyclura pinguis
Barbour (Fig. 1), on Anegada, British Virgin Islands includes remarks
regarding the sympatric Hispaniolan forms, C. ricordi (Dum6ril and
Bibron) and C. cornuta (Bonnaterre) and reviews all known literature
dealing with ethoecology of Cyclura.

Literature on C. pinguis is scarce. Schomburgk (1832) first reported
iguanas on Anegada when he mentioned having seen "Iguana sapidissima"
on the island, but it was not until 1916 that the first specimen (an adult
female) was collected by James L. Peters. Barbour (1917) subsequently
described the species as new, and in later papers he (1917, 1919, 1930,
1935, 1937) mentioned, or implied, its extreme rarity. Today his com-
ments seem unwarranted, although the species is not common. Grant
(1937) gave a brief account of stomach contents of adults, and Under-
wood (1962) supplied brief notes on their habits.

ACKNOWLEDGMENTS

I wish especially to thank my faculty advisor, Roy W. McDiarmid, for his con-
tinued patience and interest in my research and for critically reviewing the man-
uscript. I also thank Derek G. Burch, Wade C. Sherbrooke, Richard Thomas, and
Walter G. Whitford for their helpful suggestions concerning various sections. Albert
Schwartz aided in many ways, primarily through providing contacts in the Domini-
can Republic.
I am indebted to several island residents for their aid during my stay on Anegada,
especially the Levans family who provided my room and board. Aubrey Levans
and "Brasso" Norman provided much companionship and help in the field. During
my stay in the Dominican Republic, similar provisions were made by the family of
Sixto Inchaustegui of Santo Domingo. In addition, they made possible my trip to
the vicinity of Lago de Enriquillo.
James Feigl aided in preparation of the illustrations. The line drawing is by
James Seagle.
A major part of the fieldwork for this study was made possible through a Grant-
in-Aid of Research from the Society of the Sigma Xi. To this organization I extend
my sincere thanks.

Vol. 19, No. 4

CAREY: CYCLURA PINGUIS

FIGURE 2.-Map of Anegada, British Virgin Islands showing ponds and study areas.
Blackened areas are (from left) Windberg Key, Citron Bush, and The Settle-
ment. Inset shows location of Anegada (arrow) in relation to Puerto Rico (PR)
and other islands on Puerto Rican Island shelf.
DESCRIPTION OF THE ISLAND AND STUDY SITES
Anegada lies on the Puerto Rican Island Shelf, which consists primarily of Puerto
Rico, Vieques, Culebra, and the Virgin Islands (Heatwole and MacKenzie 1967).
It is the northeasternmost island on the shelf (Fig. 2), lying about 24 km north of
Virgin Gorda, and is about 15 km long and 3 km wide at its widest point.
Although lying on the same bank as the other Virgin Islands, which are volcanic
in composition and remarkably hilly, Anegada is composed almost entirely of lime-
stone, is essentially without relief, and has a maximum elevation of about 9 m. Most
of the western end is a sandy plain or salt flat with many highly saline ponds that
often inundate the area during rainy periods. The eastern and central portions are
largely eroded limestone plains, honey-combed with cavities leading beneath the
surface.
A total of 40 days (27 March-5 May 1968) was spent on Anegada, and pre-
liminary investigations for a later intensified study were carried out on the two
sympatric forms, C. ricordi and C. cornmuta. This represents about 215 hours of
actual field time. Five days (12-16 May 1968) were spent in the Dominican
Republic in the vicinity of Lago de Enriquillo, just east of Jimani near the Haitian
border. This desolate portion of the Cul de Sac is some 40 m below sea level.
The main study area on Anegada was located about 3.5 km northwest of The
Settlement (Fig. 2), a point where sandy and rocky areas meet. This plot will be
referred to as the "Citron Bush," a local name applied to the general area of which
the study site was a part. This area is roughly rectangular and encompasses about
4.93 ha (ca 12.19 acres). Boundaries are natural and may somewhat restrict
movements of iguanas to and from the area. To the south and west are large,
nearly denuded sandy areas, to the north mostly sandy beach and the Atlantic Ocean,
and to the east an extremely dense thicket. Only adult iguanas inhabit the Citron
Bush. The substrate consists almost entirely of weathered limestone projections,
soil-filled pockets, and countless natural cavities leading to caverns beneath the

1975

BULLETIN FLORIDA STATE MUSEUM

limestone. In the southwestern portion of the study plot is a small sandy area with
numerous scattered limestone boulders. The ground cover is mostly dead vegeta-
tion; e.g. leaves, cacti, logs, and brush.
The second study area was located about 2.5 km west of the Citron Bush. This
plot is known locally as Windberg Key and is a tiny, egg-shaped islet lying about
100 m off the western shore of Red Pond on the main island (Fig. 2). This islet
is 90 m long and 50 m wide at its widest point and about 0.28 ha (ca 0.69 acres).
Windberg Key was inhabited only by juvenile iguanas. The substrate is heavily
eroded and cracked aeolian limestone with few natural cavities and little sand.
Limestone boulders are scattered over much of the key. Except during the dry
season when Red Pond dries up considerably, the isolation of Windberg Key is nearly
complete.
Additional observations were made at other localities whenever the opportunity
arose; the principal ones being Cedar Well Key, Low Key, and much of eastern
Anegada. The first two areas are actually peninsulas jutting into the north and south
sides of Flamingo Pond, just west of Red Pond. Each key is about 150 m long and
100 m wide. The substrate on each is eroded limestone with many boulders.
In the Dominican Republic, observations were made along roads at localities that
appeared suitable. This was done on a day to day basis to obtain general ideas
regarding the ethoecology of C. ricordi and C. cornuta.

METHODS AND MATERIALS

An analysis of plant composition in the Citron Bush was obtained by randomly
selecting ten points in the area and counting the numerical abundance of each
species within a ten meter radius of each point; frequency, relative abundance, and
cover were determined. On Windberg Key this was done for every plant.
An entire day was usually spent at the plots, observations being made between
0700 and 1800 hours (roughly the diel activity period of C. pinguis). Investigations
of lizard population structure, density, biomass, and home range usually employ
mark and recapture techniques or at least some means of individual recognition.
Past experience with adult Cyclura species, however, argues against mark and re-
capture because the initial capture frightens an individual so much it may abandon
the area. On Cayman Brac, on two separate occasions, adult male C. macleayi cay-
manensis were captured for inspection; upon release they fled and were not seen
again. A similar experience at the beginning of my study occurred at the east end
of Anegada. Fortunately, these lizards usually exhibit several distinctive features
(scars, missing digits, color pattern, etc.) making recognition simple, even from a
distance of several meters. Most juveniles on Windberg Key were not distinctly
featured; hence marking was essential. Various designs were painted at the base
of their tails for recognition.
Iguanas and their main retreats were assigned a number. Characterizing fea-
tures, sex, age class, approximate snout-vent length (SVL) and weight (juveniles
were measured and weighed), air and substrate temperatures, position in relation
to the "center of activity" (to be discussed below), time of day, and date were
recorded.
Adult C. pinguis were secured only with some difficulty. The easiest way was
to chase them into their holes and (if the holes were short) either noose them or
annoy them until they surged from the hole and could be grabbed. Pulling iguanas
from holes often required the assistance of a native. Cyclura, as do Conolophus
in the GalApagos Islands (Carpenter 1969), often entangle their legs among roots
on the sides of the holes. This, in addition to inflation of the body, makes them
difficult to extricate. C. pinguis adults could never be approached close enough in
the open to be caught by hand or noose. Juveniles were collected by any of the
above methods or by hand as they hid beneath rocks.
All measurements were recorded to the nearest millimeter, weight to the nearest

Vol. 19, No. 4

CAREY: CYCLURA PINGUIS

0.10 of a pound and converted to kilograms. These data were secured for adults
in the Citron Bush at the conclusion of the study.
All temperatures were measured in the shade with a Schultheis quick-recording
thermometer. Body temperatures of the lizards were taken cloacally and externally
on the flank. Substrate temperatures were measured at the point occupied by the
observed iguana; air temperatures about 200 mm above that point. Water temper-
atures were taken at a depth of 150 mm.
Humidity data were gathered with a standard meteorological sling-psychrometer.
Readings were taken four times daily at a central point on the main study plot.
Food preferences were determined by analysis of stomach contents and fecal
droppings. Plants seen being consumed by C. pinguis were identified.
Unless otherwise indicated, ranges are followed by means in parentheses. Pre-
served material from Anegada and the Dominican Republic is deposited in the
collection of Albert Schwartz.
Sample sizes in this study were small. For example, only five animals were
examined for stomach contents. As inadequate as this might appear, it is absolutely
essential when investigating most Cyclura populations because of low population
numbers. Many populations are dense but very small because of specialized habitat
preferences. Sampling to the extent that most biologists would consider satisfactory
would obliterate some populations (e.g., C. macleayi lewisi on Grand Cayman or
any of the tiny-island populations in the Bahamas).

ENVIRONMENTAL CONDITIONS

CLIMATE.-In general, the climate of the Virgin Islands is tropical,
with insolation reaching its greatest intensity in the spring (Stone 1942).
The mean annual rainfall varies greatly, ranging from 88.9 to 177.8 cm

0700 1100 1500 1900

100
35 -

90 H

J 30 80 Z
X-

60 --
S20
a 25 --60
2 *u -

20
40

0700 1100 1500 1900

TIME OF DAY
FIGcmE 3.-Diel ranges and means of air temperature (black bars) and relative
humidity (white bars) in the Citron Bush, Anegada, British Virgin Islands, 27
March-5 May 1968.

1975

BULLETIN FLORIDA STATE MUSEUM

at the various stations. Two rainfall maxima occur annually, a small one
in May or June and a larger one in October.
During this study, shade temperatures were taken in the Citron Bush
at least four times daily at 0700, 1100, 1500, and 1900 hours and were
incidental to studies of activity cycles of C. pinguis. The maximum
temperature recorded during the period of observation was 33.4C on
several occasions; the minimum was 21.10C during three late-March
mornings. Ranges, means, and humidity data are given in Fig. 3. In
the Dominican Republic, temperatures in the shade ranged from lows of
29.4C to 31.10C at the beginning of Cyclura activity (around 0700
hours) to highs of 37.40C to 41.00C between 1300 and 1600 hours.
Rainfall was not measured, but showers were frequent during the
first week of the study. After 3 April it rained only five more times.
The entire West Indian region had been suffering under drought con-
ditions for some time prior to the study.

FIGURE 4.-Typical xerophytic thorn forest habitat of Cyclura in the West Indies.
Photo taken 10 February 1965 on Cayman Brac, British West Indies.

VEGETATION.-The vegetation on Anegada is typical Antillean xero-
phytic thorn forest or scrub formation (Fig. 4). The beach around
most of the island supports either shore scrub and pioneer vegetation or
mangrove, Rhizophora mangle. Vegetation on the sandy plain to the
west is rather dense and coppice-like in some areas. The loblolly tree

Vol. 19, No. 4

CAREY: CYCLURA PINGUIS

(Pisonia rotundata), boxwood (Bumelia obovata), and seagrape (Cocco-
loba uvifera) are common. Because of its porosity, the eastern rocky
plain is more arid. Principal plants are seagrape, agave (Agave sp.),
cacti (Melocactus intortus and Pilosocereus royenii) and poiknerboy
(Pithecolobium bahamense). Epiphytes such as Tillandsia utriculata
are common on trees all over the island.
The greatest concentrations of C. pinguis were in the xeric limestone
regions. Iguanas were relatively rare on the sandy plain, except on the
numerous limestone outcroppings forming peninsulas or islets in the salt
ponds. Rocky areas were possibly inhabited in preference to sandy ones
because of the abundance and diversity of refuges.
The Citron Bush is an ecotone between the sandy and rocky plains.
A composition analysis of its vegetation and that of Windberg Key ap-
pears in Table 1. The vegetations of Cedar Well Key and Low Key
are similar to that of Windberg Key.
VERTEBRATE ASSOCIATES.-Few other vertebrates inhabit Anegada.
Apparently there are no naturally occurring predators or competitors to
adult C. pinguis. However, introduced domestic animals have become

TABLE 1.-PERCENT RELATIVE ABUNDANCE, FREQUENCY, AND COVER OF VEGETATION
ON THE Two STUDY PLOTS ON ANEGADA, BRITISH VIRGIN ISLANDS, 27
MARCH-5 MAY 1968.

increasingly important in these respects (Table 2). Under pristine con-
ditions C. pinguis, at present omnivorous (albeit primarily herbivorous),
probably occupied several trophic levels concurrently. Juveniles and
eggs were probably subjected to some natural predation just as they are
today. The colubrid snake, Alsophis portoricensis anegadae, was com-
monly reported by natives to feed on juveniles, as was A. cantherigerus
on the Caymans (Carey 1966). Alsophis portoricensis also has been
reported to feed on other lizards similar in size to juvenile Cyclura
(Schmidt 1920, Grant 1932). Predatory birds such as Falco sparverius
and Buteo jamaicensis are almost certainly a constant threat to juveniles.
Hawks, owls, gulls, and herons feed on young marine iguanas, Am-
blyrhynchus cristatus, in the GalApagos (Carpenter 1966). Hatchling
Cyclura on tiny islands in the Bahamas are almost certainly vulnerable
to such predators, especially gulls and herons.
The teiid lizard, Ameiva exsul (Wolcott 1924), and several resident
passerines (e.g., Mimus) are occasional lizard-egg feeders and possibly
prey on eggs of C. pinguis. Mockingbirds (Mimus) feed on Ambly-
rhynchus eggs in the GalApagos (Carpenter 1966).
Important natural competitors of C. pinguis were presumably few
and essentially the same as those today (Table 2). Seemingly, only
herbivorous birds and insects could have competed with adult C. pinguis

Vol. 19, No. 4

CAREY: CYCLURA PINGUIS

for food, and these were probably of minor influence. Juvenile iguanas
were probably subjected to considerably more competition since they
were insectivorous as well as herbivorous. They would have been sen-
sitive not only to the feeding activities of adults and their competitors,
but also to the numerous resident insectivores (Table 2), including birds,
several lizards, and possibly a frog.
About 300 years ago the ancestors of the present native human colony
(which now numbers about 200, all living in The Settlement) arrived on
Anegada and brought dogs, cats, goats, cattle, donkeys, pigs, and sheep
with them. Although most of these animals abound on the island today,
it is impossible to detect what effect they may have had on the relation-
ships of C. pinguis with the natural fauna. Iguanas continue to occupy
the same consumer levels, but apparently now lead a more competitive
existence.
Natives say that dogs feed on both the eggs and juveniles of C. pin-
guis and occasionally will run down and kill adults. I witnessed this on
one occasion on Anegada. Dogs and domestic pigs are known to prey
on eggs and juveniles of other large iguanines (Hirth 1963a, Carpenter
1965, 1966, Rand 1968). Cats probably affect only juveniles.
Herds of goats and cattle overlap considerably with the greatest
concentrations of iguanas, feeding on brushy undergrowth and possibly
increasing exposure of juvenile iguanas to predators. In addition, elim-
ination of this brush may increase the difficulty of food procurement for
the young iguanas directly and through resulting decreases in insect
density.
Windberg Key apparently supports very little vertebrate life other
than C. pinguis. Only Anolis cristatellus wileyae, Sphaerodactylus ma-
crolepis macrolepis, Alsophis portoricensis anegadae and the Antillean
mango, Anthracothorax dominicus were in evidence. No mammals were
seen. As no domestic animals inhabit Windberg Key, it seems probable
that resident iguanas lead a more natural life than their main-island
counterparts. If the domestic animals invaded Windberg Key, C. pinguis
would very likely be eliminated.
On 13 April, I observed the morning activity of a female in the Citron
Bush. She faced southwest about 20 m from her retreat. A bananaquit,
Coereba flaveola, flitting about had no apparent influence on the iguana
until it emitted a shrill whistle. The iguana immediately turned 1800,
fled to its retreat, and entered after hesitating for a moment at the en-
trance.
A blind snake, Typhlops richardi catapontus, was collected about 80
mm below the surface just inside a cavity occupied by a male iguana.
In the Dominican Republic I frequently encountered curly-tailed lizards,

BULLETIN FLORIDA STATE MUSEUM

Leiocephalus schreibersi, about 2 m inside iguana burrows, generally
during the heat of the day or at night.
PARASITES.-No dissections were made for endoparasites in C. pinguis,
but other forms of Cyclura (carinata [Dosse 1938], macleayi cayman-
ensis and macleayi lewisi [Grant 1940b], and macleayi macleayi [Barus
et al. 1969]), host several nematode species. Cyclura ricordi and C.
cornuta, autopsied upon return from the Dominican Republic, also hosted
several nematodes. Those in C. cornuta were identified as Atractis cru-
ciata (John Lewis, pers. comm.).
I have observed ticks of various species on all of the above iguanas,
as well as on C. rileyi, C. figginsi, and C. steinegeri. Several are dis-
cussed by Robinson (1926). A series of 59 ticks taken from C. pinguis
represented a new species, Amblyomma antillorum (Kohls 1969). About
20-30 ticks per lizard were found only on adult C. pinguis, most fre-
quently in the area of the femoral pores and in the thoracic region.
No ticks were found on 17 C. ricordi examined. C. cornuta (N=
10) was infested by Amblyomma albopictum in the same areas as de-
scribed for C. pinguis.

GENERAL FEATURES OF THE LIZARDS
Cyclura pinguis is one of the largest members of the genus. There
was a highly significant difference (t=5.772; P
adult males and females in the Citron Bush (Table 4), and for all adults
for which data were obtained (t=4.359; P
Fig. 5]). Adult males in the Citron Bush averaged 534.50_ 3.88 mm
SVL; adult females 468.00 10.87 mm.
There also was a highly significant difference (t=8.000; P
body weight between adult males and females in the Citron Bush
(Table 4), and for all adults for which data was obtained (t= 6.621; P<
.01 [data extracted from Fig. 5]). Adult males in the Citron Bush aver-
aged 6.720.21 kg in body weight, adult females 4.750.13 kg.
Adults of both sexes are dull, olive-gray above with columns of tur-
quoise (sometimes green) dots (ca 2 mm in diameter) extending down-
ward from the dorsal crest to the lateral fold. Beginning at or below the
fold are reticulations of turquoise and brown, fading on the belly to blue-
cream. The head is olive-brown, the throat and gular pouch lighter.
The tail is blue dorsally, fading to dull brown posteriorly. Limbs are
blue above, each scale bordered in black, and tan to cream below.
Spines of the dorsal crest vary considerably from shades of blue to black.
Aside from being larger (Fig. 5), males have proportionally much
larger heads, with the temporal region and jowls obviously being more
"swollen." Both sexes possess a prominent, fatty dorsal ridge (Figs. 1,

Vol. 19, No. 4

CAREY: CYCLURA PINGUIS

600

550

00
S500 00
o
I 450
I--
(3 o
Z 400 o
w
-j
350-
Z o
W 300-

250
o 8
Z 200
U)

150
-A
I I I I I I I I I
I 2 3 4 5 6 7 8

BODY WEIGHT (kg)
FIGURE 5.-Length-weight relationship for Cyclura pinguis (N=22), Anegada,
British Virgin Islands. Black dots, males; white dots, females; triangle, sex
unknown.
7), although in males the ridge is somewhat higher than in females.
The above characters permit immediate recognition of sexes. In addi-
tion, the longest spines of the dorsal crest are usually about 18 mm in
males, whereas they are about 10 mm in females. Also, the tail base of
males is more laterally compressed than in females.
Cyclura ricordi is somewhat smaller than C. pinguis; the adult males
range from 315 to 400 mm (y= 355 mm, N=4) SVL, and adult females
range from 308 to 365 mm (= 340 mm, N=3).
Cyclura ricordi is powder blue to tan above, darker to black below.

BULLETIN FLORIDA STATE MUSEUM

There are four to five white bands on the flanks that are bordered in
black and end on the belly. The arms are black above, lighter below;
the legs olive-blue. The spines of the dorsal crest are blue or black ana
about 15 mm high. Juveniles are generally somewhat darker than adults.
Cyclura cornuta is the same general size as C. pinguis. Adults range
from uniform gray-brown to nearly black dorsally and lighter ventrally.
The juvenile pattern (tawny bands interspersed with cream dots) is
obscured in adults. The limbs are usually olive, the head rusty in
juveniles and dark brown in adults.
Rhinoceros iguanas are unique in that the sclerotic coats of the eyes
are light metallic brown rather than some shade of red as in all other
known extant Cyclura species. Individuals of both this and the preced-
ing species are difficult to sex externally.
The local name of all three of these lizards is "guana;" this term
apparently is uniform for all Cyclura populations throughout the West
40

y 38- 0

* *

* *

26 28 30 32 34 36 38 40

AIR TEMPERATURE *C
FIGURE 6.-Relation of ambient and body temperature at time of capture for active
Cyclura pinguis (N= 16), Anegada, British Virgin Islands.

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CAREY: CYCLURA PINGUIS

Indies, regardless of the country. On Anegada juveniles are called "four
o'clocks"
THERMAL RELATIONSHIPS
FIELD WoRK.-Because of the relatively few iguanas on Anegada and
my reluctance to upset their daily routines, temperature data for only
16 animals were obtained. These data were procured on sunny days,
usually after 1100 hours, so the lizards had ample opportunity to reach
desired activity temperatures. The distinct differential between ambient
and cloacal temperatures (Fig. 6) clearly indicates that C. pinguis is a
heliothermic lizard. In the strict sense, heliothermy merely implies that
heat gain in an ectothermic animal is obtained principally through solar
energy (Cowlcs 1940). It does not necessarily suggest that some form
of behavioral thermoregulation occurs, although that possibility is not
ruled out. Heath (1964) pointed out that even though many reptiles
are fully capable of regulating their body temperatures behaviorally,
they can also attain and retain equable temperatures without need of
active regulation. Perhaps the most striking of the several examples of
behavioral thermoregulation described for lizards is that of the marine
iguana on the GalApagos. In this species "prostrate" or "elevated"
basking postures are assumed in accordance with time of day, intensity
of solar radiation, and body temperature (Bartholomew 1966).
Behavioral thermoregulation can be seen in the daily activity pattern
of C. pinguis, which agrees closely with that seen in C. macleayi cay-
manensis (Grant 1940b, Carey 1966). Cyclura pinguis usually appears
each day shortly after 0700 hours, when ambient temperatures average
around 250C. Upon emergence they walk to the nearest patch of sun-
light and assume a prostrate basking posture similar to that described
for Amblyrhynchus. Prostrate basking in C. pinguis consists of lying flat
on the belly with the limbs extended in "spread eagle" fashion (Fig. 7).

In Amblyrhynchus the head and neck are laid flat; in C. pinguis the head
is elevated.
About 1 hour later, apparently after reaching a desired body tempera-
ture, they rise on their arms to a semielevated position. At this time
(ambient temperature ca 270C) they begin to move about in search of
food, stopping every few steps to taste bits of material around them.
Basking continues after feeding, rarely in full sun but in a sun-and-shade
mosaic among bushes, similar to that utilized by the green iguana, Iguana
iguana, at San Blas, Nayarit, M6xico (McGinnis and Brown 1966).
Throughout most midafternoons, when ambient temperatures hovered
around 300C, Cyclura pinguis was seen in partial or full shade. In later
afternoons, from 1500 to 1800 when temperatures generally dropped be-
low 300C, C. pinguis again came out into exposed places, usually near
a retreat. No iguanas were seen after this time, when temperatures
usually fell below 260C. Coolest ambient temperatures at night (usually
after 0100) averaged 220C. Iguanas observed after sunset were always
in their holes and presumed sleeping.
Elevated basking was not observed in C. pinguis, and probably would
be of little use to a form able to utilize the shade and filtered insolation
of brushy areas. On the other hand, Amblyrhynchus spends the entire
day on the barren lava coasts of the GalApagos Islands, with no shady
retreats available. Elevated postures allow them to maintain body tem-
peratures below the lethal threshold while in direct sunlight (Bartholo-
mew 1966).
Insufficient data for reliable determination of eccritic temperatures
were obtained. Cloacal temperatures secured from 16 active animals
ranged from 27.1C to 39.80C (35.290C); 56% of the records were
greater than 360C, and 25% ranged from 390C to 39.80C. This contrasts
with mean activity temperatures of 31.980C for Conolophus subcristatus,
35.130C for C. pallidus (Carpenter 1969), and 36.1C for green iguanas,
Iguana iguana (McGinnis and Brown 1966). Means slightly greater than
340C were observed by Carpenter (1966) for marine iguanas on several
islands. Bartholomew (1966) indicated a preferred temperature range of
350 to 370C for these lizards.
The first several days of the study (late March) were characterized
by cool, blustery weather that had no profound effect on C. pinguis.
Midmorning temperatures at that time averaged in the low 20's, and it
was windy and overcast. Though air temperature may have an indirect
effect on daily activity of these iguanas, it may not be the main influ-
encing factor. Milstead (1957a, b) found that light intensity and/or
soil temperature governed Cnemidophorus activity in southwestern
Texas, and this may also be true of C. pinguis.

Although torrential rains drove Cyclura pinguis into their burrows,
light steady rainfalls were apparently not annoying. Light rain may
have a desirable cooling effect, as adults were seen in the open during
several steady downpours. I have kept many Cyclura species in outdoor
enclosures in southern New Mexico, where ambient temperatures usually
exceeded 35C by noon each summer day. Adults usually basked most
of the morning. Often as I sprayed the iguanas with a garden hose, they
followed the spray around the pen for about 10 minutes and then were
wary of it. On several occasions they raised up on their toes, apparently

1.36 kg

0.82 kg

4/d

4.68 kg
\-e

a-- a

0 10 20 30 40 50 60 70

MINUTES
FIGURE 9.-Relation of heating rate to body size in Cyclura pinguis (N=3) on
Anegada, British Virgin Islands. Lizards were placed together in full sunlight at
1000 hr, 20 April 1968; maximum wind velocity about 8 km/hr.

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CAREY: CYCLURA PINGUIS

to avoid contact with the hot, sandy surface, which averaged 600C dur-
ing the hottest part of the day.
EXPERIMENTAL WoRK.-Bartholomew (1966) indicated a need for
additional experimental work on the thermal relations of large lizards.
Although a comprehensive coverage of the thermal relations of Cyclura
is beyond the scope of this paper, limited data on the heating rates of
various sized C. pinguis in relation to environmental temperatures are
useful (Figs. 8, 9). In both experiments, animals were tied at the waist
and placed in full, midmorning sunlight. The method gave them free
movement and allowed them to thermoregulate. Dorsal skin, air, and
substrate temperatures were measured at 5-minute intervals until panting
began, usually around 40 C. Panting apparently enables the animals
to remain longer within their range of thermal tolerance. The rapid
flow of air over the blood engorged tongue permits dissipation of slightly
more heat than is produced metabolically (Kour and Hutchison 1970).
Data for marine iguanas closely agree with this figure (Bartholomew
1966), but green iguanas begin panting at a slightly higher temperature
(ca 42'C) (McGinnis and Brown 1966). Frantic efforts to escape
usually accompanied panting in C. pinguis, and they were then quickly
placed in the shade.
A juvenile weighing 772 g was used to determine the relation of skin
and cloacal temperatures to air and substrate temperatures. Primary
sources of heat gain insolationn and conduction from substrate) caused
panting in forty-five minutes, at a temperature of 39.80C. Although
skin and body temperatures remained close throughout (skin was al-
ways at least 1 higher), they had nearly equalized when panting began
(Fig. 8). These data are in agreement with that obtained by Kour and
Hutchison (1970) for other lizards.
An indication of body size-heating rate relationships was obtained
by tethering three animals of different weights (0.82, 1.36, and 4.68 kg)
simultaneously. As in marine iguanas (Bartholomew 1966), rates of
heating were related inversely to body weights (Fig. 9).

RETREATS
Little has been recorded concerning retreats of Cyclura. Gosse
(1848) did not mention holes as retreats of C. lophoma ( =C. collei) on
Jamaica, but stated (upon another's observations) that they lived in
trees. Lewis (1944) observed C. lophona in trees (at least 3 m above
ground) and C. macleayi caymanensis commonly basking on Conocarpus
branches. This and the Grand Cayman form, C. macleayi lewisi, usually
favor natural cavities as retreats (Grant 1940b, Carey 1966). Climbing
has also been documented for C. rileyi on San Salvador (=Watlings

1975

BULLETIN FLORIDA STATE MUSEUM

Island) in the Bahamas (Stejneger 1903, Paulson 1966) and C. macleayi
macleayi on Cuba (Cooper 1958), but they too retreat into holes among
the rocks. Cyclura cornuta on Ile de la Petite GonAve lives in the crevi-
ces in coral rock (Klingel 1929). I saw this lizard in the hills bordering
Lago de Enriquillo in the Dominican Republic, but found that there
they dig burrows in the sand as well as in the fossil coral cliffs as earlier
reported by Noble (1923). Cyclura ricordi also burrowed in the hills
bordering the lake. On Isla Cabritos, they lived only among crevices in
rocks. Several Bahaman forms (i.e. C. nuchalis and C. carinata bartschi
[Cochran 1934], C. fiiii;,.i [Bailey 1925, Wayne King, field notes, Tony
Gran6s, pers. comm.], C. inornata [Rabb and Hayden 1957, Wayne King,
field notes], and C. baeolopha [Wayne King, field notes]) prefer natural
cavities. Sutcliffe (1952) and Hardy (1956) observed both burrowing
and retreating to limestone cavities in C. macleayi macleayi in Cuba and
adjacent islands. Burrows extended to nearly 3 m in length and had no
enlarged chambers. Burrows of C. ricordi and C. cornuta were much
longer (ca 10 m) and also lacked chambers.
In the Citron Bush, C. pinguis used burrows or natural cavities in
the limestone, excavations beneath large limestone slabs, or cavities
formed under large overlapping slabs that were raised slightly by the root
system of a loblolly tree (Pisonia rotundata) as refuges. Only one adult
male was observed outside of a limestone area. His retreat was a bur-
row, presumably self-excavated.
Immatures on Windberg Key used only slabs as retreats. A single
slab often harbored as many as five iguanas beneath it. A very young
individual in The Settlement lived in a pile of debris in an abandoned
hut, and I never observed it more than a few meters from the debris.
Refuge entrance sizes ranged from holes just large enough for an
adult to squeeze through to some much larger than an iguana. Refuges
ran parallel to the surface, usually not more than 1 m deep, and varied
in length from a minimum of about 2 m to an indeterminate maximum
far into the limestone. Refuges contained moist soil and forest litter in
the immediate interiors, with swarms of mosquitos at the entrances and
in the moist interiors.
Excavations in limestone slabs probably offer considerably less se-
curity because of the short distance between entrance and terminal
chamber (often less than 2 m), but still provided sufficient concealment.
A typical slab was about 4 m2 and about .25 m thick.
Cavities formed by roots of loblolly trees seem to offer much more
security. The roots grew beneath and onto the slabs, forming extremely
sturdy refuges. The cavities were not deep, but wound around wherever
roots were growing, to form a maze.

Vol. 19, No. 4

CAREY: CYCLURA PINGUIS

Cyclura macleayi macleayi (Buide 1951) and C. macleayi cayman-
ensis (Carey 1966) flee from intruders in short spurts, repeatedly stop-
ping to bobb and hiss, while Cyclura pinguis rushes directly to the hole,
rarely hesitating at the entrance. Both C. ricordi and C. cornuta re-
treat in spurts before finally entering their burrows, as does Conolophus
in the Galapagos Islands (Carpenter 1969).
Once C. pinguis individuals enter their holes, they may not come
out for a surprisingly long time. When I approached the Citron Bush at
0900 on 14 April, an adult female entered her refuge and stayed there.
At 1345 I found her still lying in the terminal chamber. On 19 April
an adult male reemerged 2 hours and 47 minutes after having taken
refuge.
It is well known that marine iguanas enter the sea for feeding pur-
poses, but they will not willingly enter the sea for escape unless their
body temperatures are approximately that of the water (Bartholomew
1966). An iguana just leaving the sea will quickly drop back if ap-
proached, but a basking individual cannot be induced to retreat to the
water.
Only C. cornuta (Noble 1923) and C. macleayi macleayi (Hardy
1956, Lando and Williams 1969) are known to retreat to water. Gosse
(1848) stated that his captive C. lophoma ( = C. collei) readily took to
water, but not necessarily as a retreat. An adult male C. pinguis on
Cistern Well Key often entered the water when disturbed. Temperature
seemed to have little influence on his behavior. On 7 April, after re-
cording his cloacal temperature, I placed him on the ground, and he
immediately took flight into Red Pond. At that time his cloacal tem-
perature was 40.20C and the water was 27.50C. He tried to dive, but
the water was too shallow. On the morning of 12 April, his tempera-
ture was 37.0C and the water was 27.9C. Upon release his behavior
was identical to that described above. On four subsequent occasions he
entered the water upon my approach. I assume, therefore, that Cy-
clura, unlike Amblyrhynchus, can and will use water as a retreat regard-
less of the difference between body and water temperature.

dea littoralis) (Grant 1940b). On Cayman Brac they often raid culti-
vated areas, feeding on potato vine, plums, mangoes, and fallen pawpaws
(Grant 1940b, Carey 1966). Cyclura stejnegeri on Isla Mona was ob-
served feeding on Tribulus cistoides (Martin 1966). The literature is
extensive regarding the herbivorous habits of other iguanine genera.
Examination of stomach contents of five animals revealed that vegeta-
tion composed a major part of the diet of adult C. pinguis (Table 3).
Grasses and leaves were the most common items. Analysis of scat com-
position supplemented this analysis, although most of the plant material
was unidentifiable. One adult female (400 mm SVL) contained four
lepidopteran larvae, each about 75 mm long and 12 mm in diameter.
Grant (1937) found seagrape leaves, cactus fruit, and "wild nutmegs"
in the stomachs of two adults. Underwood (1962) suggested that
C. pinguis fed on cactus shoots, fruits, and seagrapes.
TABLE 3.-STOMACH CONTENTS OF ADULT Cyclura pinguis (N=5), ANEGADA,
BRITISH VIRGIN ISLANDS, INDICATING FREQUENCY AND VOLUME PERCENT.
Percent Percent
Food Frequency Volume
Plants
Conocarpus erectus 60 19
Coccoloba uvifera 20 12
Lantana reticulata 20 4
Reynosia uncinata 40 20
Erithalis fruticosa 40 6
Grasses 20 10
Unidentified 100 14
Insects
Lepidoptera larvae 20 15
Stomachs of juvenile C. pinguis were not examined. It is quite pos-
sible that insects form the major food item. Juveniles of several Cyclura
species cornutaa, figginsi, inornata, macleayi, pinguis, ricordi) kept in the
laboratory at various times have shown a marked preference for insects
(esp. crickets, grasshoppers, and mealworms) over plant material. In-
sects are a major food source for Ctenosaura similis juveniles in Guana-
caste Province, Costa Rica (Roy W. McDiarmid and Dennis R. Paulson,
unpubl. data). In addition to most fruits and vegetables, captive
C. pinguis adults feed on canned dog food and laboratory mice and rats.
Cyclura pinguis is an active forager. Following basking in the morn-
ing they move quickly about an area, hesitating every few steps to taste
particular objects (pebbles, plants, etc.) in their path. They feed in
typical iguanine fashion, snapping off leaves and flowers with a twist of
the head or by the jaws alone, often using their forefeet to pull a food
item closer. They occasionally climb into low bushes to feed. I saw
them actively feeding on the leaves of Conocarpus erectus, Coccoloba
uvifera, and Pisonia rotundata.

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CAREY: CYCLURA PINGUIS

Stomachs of C. ricordi and C. cornuta contained exclusively fruits
of unidentified cacti. None were observed feeding in the field. In cap-
tivity, feeding is identical to that of C. pinguis.
"Sneezing" fluid from the nostrils in the form of a fine salt spray
was common in each of these rock iguana species. As in other iguanines
(Templeton 1964, 1967), this probably is an extrarenal mechanism for
ridding the body of excess salt.

HOME RANGE

SELECTION OF HOME RANGES.-Natural cavities (Fig. 10) and loblolly
trees occurred in nearly all home ranges of adult iguanas, and because
both form refuges it appears that shelter is an important factor in home
range selection. In addition, iguanas were occasionally observed resting
on the lower (2-3 m high) branches of these trees, as well as in the shade
beneath the trees. Though loblolly leaves were never found in stomachs,
an adult male was once seen nibbling them.
Selection of mates may also influence the choice of home range sites.
An area must be chosen that has sufficient available food as well as

refuges, because pairs usually occupy overlapping home ranges. All ob-
served pairs on Anegada had refuges 23 m or less apart. One pair (male
5 and female 5) occupied the same retreat.
It has been documented previously (Fitch 1940, Stebbins 1944, Blair
1960, Hirth 1963b, Tinkle 1967) that within the home range of some
lizards all daily movements are made from a center of activity. It may
serve as a feeding site, place of refuge, or simply as a basking site.
The center of activity is not necessarily the geometric center of the home
range, though, with one exception, that of C. pinguis in the Citron Bush
was approximately so. The center of activity of adult iguanas in the
Citron Bush was their place of refuge; the trees, the cavities, or both.
All travels were made from these refuges and, upon disturbance, the
animals immediately returned. Feeding and basking took place at almost
any site within the home range, but there seemed to be preferred sites
for these activities also.
Several workers (Blair 1960, Tinkle et al. 1962, Carpenter 1966)
have seen females of some lizards laying their eggs outside of their nor-
mal activity area. The first authors suggested that this behavior might
be instrumental in the dispersal of hatchlings throughout the population.
It is likely that the same behavior will be demonstrated for C. pinguis,
although it was never directly observed. Home ranges of immatures
never overlapped those of adults. In fact no young of any age were
observed closer than several hundred meters to the nearest known adults.
One immature (probably a hatchling from the previous year) lived in
The Settlement, at least 3 km from the nearest known adult. On Cay-
man Brac, juvenile C. macleayi caymanensis were found only in the
settlement of West End, about 5 km from the adult population (Carey
1966). C. Rhea Warren (pers. comm.) collected juvenile iguanas at
the airport on Cayman Brac, about 5.5 km from the nearest known adults.
Natives on both Anegada and Cayman Brac report that females lay
eggs in the sandy periphery of each village. I saw a juvenile C. macleayi
lewisi on Grand Cayman living in a stone fence near native houses,
over 4 km from the adults. According to natives, females lay eggs in
sandy areas inland from the rocky beach, more than 5 km from any
known adults. The attraction to settlements is probably the increased
density of insects. In the Dominican Republic, juveniles of C. ricordi
were seen at the same localities as adults, who apparently have no indi-
vidual territories.
Each year scores of female green iguanas (Iguana iguana) on Barro
Colorado Island, Canal Zone, migrate to the tiny island of Slothia in
Gatun Lake to lay their eggs (Rand 1968). Rand suggested that this
communal nesting results from lack of desirable sites on Barro Colorado

Vol. 19, No. 4

CAREY: CYCLURA PINGUIS

as a result of high population density. Also, migration to the islet serves
to decrease predation, which is great on Barro Colorado.
Because some Cyclura females may travel substantial distances to lay
their eggs, it is possible that C. pinguis on Windberg Key hatched there
rather than colonizing the islet. There is no evidence for aggregate
nesting. However, such nesting habits have been observed in Ambly-
rhynchus cristatus in the Galapagos (Carpenter 1966), C. cornuta on
Isla Beata, off the southwestern tip of the Dominican Republic (Noble
1923), and C. stejnegeri on Isla Mona (Richard Thomas, pers. comm.).
All of these are high-density populations.
The principal reasons suggested for nesting on Slothia presently do
not hold for iguanas on Anegada. There are many seemingly desirable
laying areas other than Windberg Key, and predation on females or eggs
other than by such unnatural predators as dogs must be of low magni-
tude.
The north, south, and east shores of Windberg Key, though very
rocky, are a tangle of buttonwood (Conocarpus erectus). Activity of the
young iguanas is almost completely confined to this protective mass of
vegetation. The large slab under which these lizards usually take refuge
is located on the east shore amongst the buttonwood. They were oc-
casionally seen basking on the grassy interior of the island. The center
of activity would be difficult to designate since the entire tangle of but-
tonwood was used, with few excursions from it. The only suitable laying
site was the sandy area on the west shore.
A juvenile in The Settlement lived in a debris pile inside an aban-
doned hut. This hut was clearly its center of activity, because it
ventured only a few meters away from it each day to feed and bask and
fled back to it at the slightest disturbance.
ADULT HOME RANGES.-Home range estimates for adults were ob-
tained using a slightly modified minimum convex polygon method
(Tinkle et al. 1962). This method entails connecting the outermost
points of recapture on graph paper to form a convex polygon, then esti-
mating the minimum home range by computing the enclosed area by
any of several techniques. In this study, sightings were used instead of
recaptures, and home range areas (Fig. 10) were determined by the
extrapolation technique first used for lizards by Jenssen (1970). Home
ranges were plotted on graph paper of tested weight consistency (5
pieces of equal size within 0.003 g of each other on a Mettler balance).
The plotted home ranges were then cut and weighed on the balance
against a piece from the same paper scaled to a known area (334.45 m').
The results closely agree with those obtained by employing a planimeter.
Although territoriality was not directly observed in this study, aggres-

BULLETIN FLORIDA STATE MUSEUM Vol. 19, No. 4

sive behavior is common in iguanids and spacing (members of the same
sex separated and those of opposite sex overlapped [Fig. 10]) implies
such intraspecific interactions. All iguanas observed in the Citron Bush
remained on their home ranges throughout the study. Hence permanent
residency in the area during the period of study was assumed.
Males occupied home ranges from 116.06 to 985.11 m2 (546.61
160.46 m2; N= 5); female ranges were from 155.47 to 412.31 m2 (276.48-
41.62 m2; N=5) (Table 4). The difference was not significant nor was
the product-moment correlation coefficient r value between the log, of
the body weights versus the log, of home range areas (males and females
treated both separately and together). This is difficult to explain bio-
logically, because males were significantly longer and heavier than fe-
males. It has been shown that home ranges of birds (Armstrong 1965,
Schoener 1968), mammals (McNab 1963), and reptiles (Turner, Jenn-
rich, and Weintraub 1969) are most always related to body weight. As
males in all of these classes usually are larger than females, males should
occupy larger home ranges. This has been demonstrated already in
several lizards (see literature reviews in Tinkle 1967 and Turner et al.
1969; Jenssen 1970).
TABLE 4.-HOME RANGE AND LIZARD SIZES FOR ALL ADULT Cyclura pinguis IN THE
CITRON BUSH, ANEGADA, BRITISH VIRGIN ISLANDS.
Snout-Vent Weight Number Home Range
Individual Length (mm) (kg) Observations Area (m')
MALES
2 545 7.17 6 846.34
1 539 6.95 7 116.06
5 536 6.81 4 985.11
4 531 6.72 3 401.46
3 522 5.95 3 384.09
X = 534.60 6.72 4.60 546.61
FEMALES
4 487 5.13 4 241.98
1 481 4.86 10 155.47
3 426 4.77 4 295.42
5 470 4.68 3 412.31
2 476 4.31 3 277.21
X = 468.00 4.75 4.80 276.48
The lack of significant size difference in C. pinguis is probably the
result of the small sample sizes (five for each sex), leading to extremely
high variances. The number of recaptures (sightings in this case) in
each sample is quite low also (Table 4). One disadvantage of the mini-
mum convex polygon method of determining home range area is that
estimates of home range size tend to increase as the recapture numbers
increase (Jennrich and Turner 1969). However in this study, the high-
est number of sightings within each sample yielded the smallest home

CAREY: CYCLURA PINGUIS

range estimates! In the above paper, Jennrich and Turner provided a
correction factor for estimates based on the minimum polygon method,
but with few observations. I applied this correction factor to my data
but found that the new estimates, when added together, were 16 percent
larger than the entire study area (bear in mind boundaries are natural).
I concluded that my original home range estimates are likely minimum.
However, the fact that low estimates persist as the number of sightings
increases all but negates the probability that the estimates would increase
significantly with additional sightings. If energy needs control home
range size (see below for discussion), herbivory as seen in these iguanas
might preclude any need for movements outside the rather small areas
shown. It seems that the correction factor of Jennrich and Turner takes
into account only the correlation of low home range estimates with few
observations, and not the biology of the occupants of those home ranges.
At a reduced probability level the difference in home range area be-
tween males and females is significant (t'= 1.630; P
calculated when sample variances are heterogenous [Steel and Torrie
1960: 81]). I suspect that if sample sizes were larger (in this case only 5
males and 5 females were observed), males would be shown to occupy
significantly larger home ranges than females. Also, since some (prob-
ably all) females in the Citron Bush proved to be gravid, this may have
temporarily forced them into additional areas because of increased energy
demands.
The t- and t'- tests for body weight and home range area indicate that
males occupy larger home ranges simply because they are larger than
females and need more area for energy harvest. Correlation coefficients
for the log,, of body weight versus the log,, of home range area are low,
indicating that body weight may not be a principal factor (although
again this could be a product of low sample sizes), but that other para-
meters may contribute to males having larger home ranges than females.
Male lizards usually are more active than females, especially during
the breeding season, but this may be true only for polygamous species.
In animals that mate for life (which may be the case here) this would
less frequently be a factor, and in territorial forms, males would be apt
to patrol more.
Still, the most important factor governing home range or territory
size appears to be energy needs. Within the vertebrates, it has been
shown that carnivores require more room for food gathering than her-
bivores or omnivores due to the usually higher relative density of food
for the latter (St. Girons and St. Girons 1959, McNab 1963, Schoener
1968, Turner et al. 1969). McNab found that carnivorous mammals of
a particular weight required home ranges about four times that of herbiv-
orous mammals of the same body weight.

1975

BULLETIN FLORIDA STATE MUSEUM

As most lizard studies have been conducted on small insectivorous
species, comparisons with C. pinguis are difficult. Almost all of these
small insectivores (e.g., Cnemidophorus, Eumeces, Sceloporus, Uta, etc.
[Turner et al. 1969]) occupy home ranges markedly larger than that of
C. pinguis. The only herbivore with available data is the chuckwalla,
Sauromalus obesus (Johnson 1965). Males of this species are about
1/32 the body weight of C. pinguis males and occupy home ranges
averaging nearly 10 times those of male C. pinguis. This difference likely
reflects the much denser vegetation in the study area of the iguana. The
desert monitor, Varanus griseus, a carnivorous lizard intermediate in
weight between the two forms discussed above, occupies home ranges
varying from 2 to 5 km2 (data converted from Turner et al. 1969), nearly
10,000 times the home range size of male C. pinguis.
Between home ranges occupied by iguanas of the same sex, there are
"neutral zones," or undefended areas apparently used by residents of
adjacent territories primarily for feeding (Gordon 1943). In lizards,
utilization of neutral zones has been reported for Agama agama (Harris
1964) and Scelporus merriami (Milstead 1970). Three S. merriami
males foraged in a neutral area with no antagonistic encounters; when
territorial boundaries were crossed away from the area, antagonistic
encounters occurred. Milstead attributed the lack of antagonism to the
fact that the three males were outside their territories and thus not de-
fensive. In this paper the phrase unutilizedd zone",will be used in place
of neutral zone, because I have not proven that territoriality exists in
C. pinguis and thus cannot unequivocally state that the zones are unde-
fended.
Although my home range data indicate that much of the Citron Bush
is unutilized (Fig. 10), I once saw these zones occupied. On 30 April,
an adult male and female I had not seen previously were feeding several
meters from the east boundary of the home range of adult male No. 5.
Upon disturbance they fled the area and were not seen again.
JUVENILES HOME RANGES.-On Windberg Key the study of home
range behavior in juveniles was conducted as described for adults, but
juvenile home ranges broadly overlapped. In fact, all inhabitants of
Windberg Key used the same limestone slab for retreat! Subsequently,
I concluded that each iguana was utilizing the entire islet as its home
range.

POPULATION DENSITY AND BIOMASS
Relatively low population numbers and the large size of these lizards
permitted use of the total count method to estimate population density.
Individual features were used in recognition.

Vol. 19, No. 4

CAREY: CYCLURA PINGUIS

Population density did not seem to fluctuate in the Citron Bush during
the observation period. Two transients were seen in the unutilized zones,
but apparently neither took up residence there. The presence in the
Citron Bush and much of Anegada of seemingly suitable but unoccupied
habitat must be due to low density of the lizards.
The area of the Citron Bush study site was 4.93 hectares (ha) (ca
12.19 acres) and for Windberg Key 0.28 ha (ca 0.69 acres). The Citron
Bush had 10 adult iguanas, or 2.03/ha (0.82/acre); Windberg Key had
7 juvenile iguanas, or 25.00/ha (10.14/acre).
Biomass was determined at the completion of the study by capturing
and weighing each animal. The Citron Bush supported 57.35 kg of adult
iguanas or 11.63 kg/ha (4.70 kg/acre) and Windberg Key 5.90 kg of
immatures or 21.07 kg/ha (8.55 kg/acre).
Tinkle (1967) recently summarized the literature on lizard population
density. Cyclura pinguis has the lowest density of the few lizards for
which data are available. Data on lizard biomass are scarce in the litera-
ture. Cyclura pinguis biomass/acre is about 10 times greater than that
of a Kansas population of Eumeces fasciatus (ca 454 g/acre, Fitch 1954),
and Anolis nebulosus from Nayarit, Mexico (ca 488 g/acre, Jenssen
1970). However food selection and size of the animals must be con-
sidered in the comparison.
One might expect that the relatively low population density of C.
pinguis in comparison to much smaller lizards is due to their great size.
Since the C. pinguis population is apparently below the carrying ca-
pacity, the density figures are somewhat misleading. Should population
density increase, unutilized zones probably would disappear. Continued
increase could result in reduced home range size. According to Tinkle
(1967) and Hunsaker and Burrage (1969), at this point territorial be-
havior might shift to a social hierarchy. Hunsaker and Burrage suggest
that a continuum exists between these two social systems. Hierarchies
in iguanines have been observed in Amblyrhynchus cristatus (Schmidt
1935, Carpenter 1966) under natural circumstances, and in Ctenosaura
pectinata (Evans 1951), which shifted from a territorial system in re-
sponse to increased population density resulting from a rapid increase
in food (domestic crop). Hunsaker and Burrage (1969) reported an
intergeneric social hierarchy amongst several penned iguanines in the
San Diego Zoo. These authors postulated that a continuum would be
advantageous, because a species could react rapidly to environmental
constraints or sudden increases in space and available food. Social
hierarchies apparently also serve to prevent density increase by restricting
breeding to dominant animals (Tinkle 1967). Perhaps the groups of
iguanas observed on Ile de la Petite Gonave, Haiti (8 C. cornuta)

BULLETIN FLORIDA STATE MUSEUM

(Klingel 1929) and Cayo de la Piedra, Cuba (4 C. macleayi macleayi)
(Sutcliffe 1952) represent social hierarchies. Studies of C. ricordi in
the Dominican Republic suggest some sort of gregarious social structure.
Though animals were not seen in groups, their burrows were numerous
and less than one meter apart in some places. Juvenile C. ricordi com-
monly were seen in the area, indicating a population structure different
from C. pinguis.
Possibly some form of hierarchy existed on Windberg Key, even
though the residents were immature. Limited access to and from Wind-
berg Key restricted the movements of hatchlings. Distribution of the
vegetation and other resources, following division of the habitat into
home ranges or territories, might preclude the availability of sufficient
resources for every resident. An hierarchial system would permit graz-
ing over the entire key, alleviating the problem, but there were still in-
dications that the two largest inhabitants (314 and 344 mm SVL) were
undernourished. Both were lean and bony, with heads proportionally
larger than their bodies. Iguanas of equivalent size on the main island
were of normal proportions. The skeleton of another iguana of this size
class was found on Windberg. The cause of death could not be deter-
mined; possibly it died of starvation.
I observed no antagonistic encounters on Windberg Key, but I did
observe such behavior in the laboratory. Three Cyclura were kept in a
pen 2.25 m2. A large C. macleayi macleayi (female, 325 mm SVL)
usually displaced the smaller C. pinguis (female, 240 mm SVL) and
C. cornuta (sex ?, 243 SVL) at the feeding pan and basking sites by
bobbing and nipping. Cyclura pinguis displaced C. cornuta in the same
way. These data suggest that C. pinguis could develop an hierarchial
system, given the necessary circumstances.

POPULATION STRUCTURE AND REPRODUCTION

BREEDING STRUCTURE.-The sex ratio of adult iguanas in the Citron
Bush (and at other localities periodically checked) remained a constant
1:1 (5 males, 5 females) throughout the study. In most cases (80%-
Citron Bush; 82.4%-Combined sites), a female was seen in company
with, or at least in close proximity to, a male. Each case of suspected
pairing in the Citron Bush was confirmed by overlapping activity areas
(Fig. 10). On 29 March and 25 April, I watched the lone pair on Cedar
Well Key feeding side by side. Each time they were disturbed they
fled to their respective retreats (located only a few meters apart). On
30 April, I observed a male and female on Low Key walking together

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CAREY: CYCLURA PINGUIS

across an area of sparse vegetation. The male trailed the female by
about 2 m.
These observations suggest monogamy. This type of breeding system
may be a result of intrasexual antagonism, as in Uta stansburiana
(Tinkle 1967). The layout of home ranges in the Citron Bush suggests
intrasexual antagonism and secondary monogamy in C. pinguis, but this
kind of nonobligatory monogamy should be more common in populations
approaching maximum density. In depleted populations, such as those of
C. pinguis, pressure is lessened and residents have more choice in mate
selection since more area could be covered uncontested. Nevertheless,
abnormally low population numbers might retain monogamy at the
facultative level, since the number of unpaired animals would be limited.
Nothing is known about duration of pairing in C. pinguis. Barring
disturbances refuges utilized by pairs were usually permanently occupied.
Females usually outnumber males in populations of adult lizards
(Blair 1960, Hirth 1963b, Harris 1964, Tinkle 1967), but only one un-
paired C. pinguis female was seen in the Citron Bush and an unpaired
male was present in the same general area (Fig. 10). All unpaired
S adults observed elsewhere on Anegada were males. Except in one case,
the large sizes and general appearance of the females indicated advanced
ages. Mortality may affect females more severely than it does males
because of increased exposure of females to predators during egg-laying
trips. Females distended with eggs would be hampered in their move-
ments, and may also be less wary during this time. Carpenter (1966)
observed the laying behavior of female marine iguanas by tunneling
into egg-laying burrows from the side without being noticed by the
females. Female desert iguanas, Dipsosaurus dorsalis, remain under-
ground while carrying eggs (Norris 1953).
Female deaths from cave-in of the burrows have been reported for
marine and green iguanas (Carpenter 1966, Rand 1968). The burrowing
behavior of captive female Cyclura macleayi macleayi is similar to that
of marine and green iguanas (Shaw 1954), all digging tunnels about 1 m
long. C. cornuta on Isla Beata (Noble 1923) and C. figginsi on Guana
Cay, Bahamas (Chris Coencn, unpubl. data) excavate egg burrows
about 0.6 m long. Haast (1969) reported that a female C. cornuta de-
posited her clutch in a tunnel 0.4 m long.
REPRODUCTION.-Three female C. pinguis (476, 426, 400 mm SVL)
contained enlarged, yolk-filled ovarian follicles, whereas three females
measuring less than 400 mm SVL were reproductively inactive. Al-
though the sample was too small to determine accurately the size at
which females become reproductive, all observed females exceeding 400
mm SVL were considered adults. Because of considerable hiatus be-

BULLETIN FLORIDA STATE MUSEUM

tween the largest individuals (314-344 mm SVL) without yolk-filled
follicles and the smallest individual (400 mm SVL) with such follicles,
sexual maturity must be attained between 350 and 400 mm. Males of
equivalent size or larger were considered adults.
Lack (1967) stated that female size and clutch size are correlated in
many species of animals. This holds both intra- and interspecifically for
all species of lizards for which reproductive data are available (Tinkle
et al. 1970). My limited C. pinguis data also tend to support this rela-
tionship. In three adults examined, the largest female contained 16
yolked follicles, the intermediate 14, and the smallest 12. These ova
ranged from 23 to 34 mm (31.53 mm) by 25 to 29 mm (27.23 mm), 30
to 34 mm (32.54 mm) by 24 to 29 mm (27.26 mm), and 31 to 34 mm
(32.67 mm) by 23 to 29 mm (26.92 mm), respectively.
Stejneger (1903) reported five eggs in a female C. rileyi collected 13
July 1903 on San Salvador, Bahamas. Female C. macleayi caymancnsis
lay 8 20 eggs in May or June (Grant 1940b). Grant suggested a similar
laying period for C. macleayi lewisi. Cyclura collei females lay about 20
eggs in April or May (Lewis 1944, 1946). Street (1952) reported 16
eggs laid by a C. macleayi macleayi on Cuba. On 10 July 1953, a female
of the same species in the San Diego Zoo laid 17 eggs averaging 65.6
mm by 44.5 mm. This female and another were bred to captive males
in June of the previous year; oviposition of an unstated number of eggs
occurred about a month later (Shaw 1954). Cyclura cornuta females lay
about 17 eggs each on Isla Beata (Noble 1923). Captives of this species
laid clutches of 16 (x= 70.20 by 45.30 mm), 11 (Y= 66.72 by 45.21 mm),
23 (x=68.35 by 46.67 mm), and 20 eggs in July and August in the San
Diego Zoo and the Miami Serpentarium (Haast 1969, Shaw 1969). A
nest of C. stejnegeri investigated by Richard Thomas on Isla Mona on
14 July 1965 contained 12 eggs, one of which measured 78 by 47 mm.
A female C. figginsi (290 mm SVL) collected on 3 February 1967 on an
unnamed Exuman cay about 5 km northeast of Great Exuma, Bahamas,
contained 7 enlarged follicles. Clutch sizes of C. figginsi on Guana Cay
numbered 3 to 4 eggs; oviposition occurred in early to mid-June (1970)
(Chris Coenen, pers. comm.). Three female C. ricordi (365, 347. and
308 mm SVL) collected on or about 14 May 1968 in the Dominican Re-
public contained 6, 4, and 4 yolk-filled ovarian follicles, respectively.
All females of C. figginsi, C. pinguis, and C. ricordi examined for re-
productive condition contained, in addition to maturing ova, a nearly
equal complement of follicles about one quarter the size of the maturing
ones. Determination of the significance of these smaller follicles is diffi-
cult. They may represent a second clutch for that year, or the next sea-
son's clutch. However, Tinkle et al. (1970) showed that late-maturing

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CAREY: CYCLURA PINGUIS

lizards usually are not multiple-brooded. Compensatoin for fecundity
loss in C. pinguis is another possibility, but populations of C. figginsi
and C. ricordi are not known to be disturbed, yet they too possess a
second group of maturing eggs. Insular lizards, which apparently live
to rather advanced ages with little or no natural predation on adults
(hence low adult mortality rate), seemingly would have little need for
more than one clutch per year. It is possible that natural juvenile mor-
tality may be greater than suspected. Further study is needed to satis-
factorily solve this problem.
A clutch of 16 C. macleayi macleayi eggs in Cuba required 93 days
to hatch (Street 1952). The clutch of 17 eggs from a captive C. macleayi
macleayi began hatching after 119 days (Shaw 1954). Noble (1923)
postulated 9 weeks for hatching in C. cornuta on Isla Beata. The
clutches of 16, 11, and 23 eggs of C. cornuta in the San Diego Zoo began
hatching after 106, 111, and 115 days (Shaw 1969). In the Miami Ser-
pentarium a clutch of 20 eggs required 125 days to hatch (Haast 1969).
Judging from the size of ova in C. pinguis, the eggs may have been
near ovulation. Oviposition probably occurs in April, May, or June, and,
allowing 90-120 days for incubation, hatching would then occur in August
or September.
Fitch (1970) stated that the giant iguanas inhabiting the drier parts
of the tropics synchronize their yearly breeding seasons with the time of
maximum rainfall. Ctenosaura and Iguana generally lay their eggs dur-
ing the dry season to take advantage of maximum incubation tempera-
tures (Davis and Smith 1953, Alvarez del Toro 1960, Hirth 1963a, Rand
1968). The young hatch during the early rainy season, a period of
denser vegetation and more abundant insect food. A similar laying
schedule is followed by Basiliscus vittatus (Alvarez del Toro 1960, Hirth
1963b). In Amblyrhynchus, oviposition occurs toward the end of the
rainy season (January or February) (Carpenter 1966). Carpenter sug-
gested that the breeding cycle is timed to avoid the garria season, a four
month period of heavy mist and cool temperatures beginning in June.
Similar timing may be operating in Conolophus pallidus on Barrington
Island, Galapagos; females contain leathery-shelled oviducal eggs in De-
cember (Slevin 1935).
Cyclura also seems to lay in synchronization with periods of maxi-
mum rainfall, but in a somewhat different pattern than that documented
for other tropical iguanas. Captive C. macleayi macleayi and C. cornuta
lay in mid to late summer, about the time of maximum rainfall on their
native islands. Cyclura figginsi on Guana Cay excavate burrows in early
June, several days prior to the beginning of the rainy season (Chris

1975

BULLETIN FLORIDA STATE MUSEUM

Coenen, pers. comm.). The females remain by the nests until the first
rains, then oviposit and bury the eggs.
Cyclura pinguis females apparently oviposit at the beginning of the
rainy season (April or May) with hatching occurring 3 to 4 months later.
In general, rainfall in the Virgin Islands is at its heaviest from May to
November, with the lower of two maxima occurring in May and June
and the higher in October (Stone 1942). The increased moisture may
prevent dessication of the eggs during incubation, as well as increasing
plant growth and insect abundance, to assure an adequate food supply
when the hatchlings appear.
ADDITIONAL NOTES ON NESTING.-Nest guarding by Cyclura females in
the San Diego Zoo has been recorded. Cyclura macleayi macleayi females
attempted to drive off would-be nest molesters (other large lizards and
humans) with vigorous bobbing and open-mouthed charging (Shaw
1954). Under similar circumstances, C. cornuta females repeatedly ap-
proached molesters but did not attack (Shaw 1969). Similar behavior
has been reported for marine and green iguanas (Carpenter 1966, Rand
1968). Cyclura figginsi females on Guana Cay reportedly guarded a
previously excavated burrow from other females while waiting for the
rains to begin (Chris Coenen, unpubl. data). It is not known whether
they guarded the nest after oviposition.
AGE AT MATURITY AND REPRODUCTIVE POTENTIAL.-Sexual maturity
probably is not reached for several years following hatching. Fitch
(1970) postulated 3 years as the minimum breeding age for Ctenosaura
similis, an iguanine species smaller than C. pinguis. He based this esti-
mate on the fact that young thought to be 9 months old were still less
than half grown and coexisted with young seemingly belonging to the
next oldest age group. Mayhew (1971) postulated a 5 or 6 year matura-
tion period for Dipsosaurus dorsalis, smallest of the iguanines, based on
the average growth rate of captive and wild juveniles and a known SVL
upon attaining maturity. Employing this method, a minimum maturing
period of 7 to 9 years can be speculated for C. pinguis. Two subadult
specimens were maintained in captivity for 10 months on an 8 hour per
day photoperiod and food ad libitum. Mean growth rates were 1.17
and 2.97 mm per month; a maximum growth rate of 3 mm per month
for C. pinguis (of this age-group) in the wild was then assumed. The
SVL of C. pinguis hatchlings is unknown. The lone main island juvenile
measured (ca 6 months old if presumed date of hatching is correct)
was 117 mm SVL, suggesting a SVL of about 100 mm at hatching.
Hatchlings of C. macleayi macleayi and C. cornuta (iguanas equivalent
in adult size to C. pinguis) in the San Diego Zoo ranged from 95 to 100
mm SVL (Shaw 1954, 1969). As it appears that maturity in C. pinguis

Vol. 19, No. 4

CAREY: CYCLURA PINGUIS

is attained at or around 400 mm SVL, 7-9 years would be required to
reach this size at a growth rate of 3 mm per month.
As all examined C. pinguis females exceeding 400 mm SVL were re-
productively mature and paired, it seems that all pairs on Anegada were
potential producers of offspring. Reproductive potential was determined
on the basis of the number of enlarged yolk-filled follicles. This po-
tential is influenced by size and age of the females, age at initial repro-
duction, number of clutches, and the number of reproductive females in
the population. There is no reliable method for aging iguanas, so re-
productive potential can be crudely estimated only for adult females.
Three adult females in the Citron Bush had an average of 14 enlarged
ovarian follicles. If only one clutch per year is deposited, potential re-
production of the five females in the Citron Bush was roughly 70 off-
spring for 1968.
Considering the low density of C. pinguis in the Citron Bush and
probable slow rate of adult turnover, environmental resistance against
that potential production appears great. The differential between poten-
tial production and the actual number of offspring reaching sexual ma-
turity can probably be attributed to predation. In addition, parasitism
might also affect iguana eggs on Anegada; such a condition was described
for marine iguana eggs on the Gal~pagos (Carpenter 1966).
Miscellaneous egg and juvenile mortality factors reported in other
species of Cyclhra could be the same for C. pinglis. All but one of the
17 eggs laid by captive C. macleayi macleayi hatched, but five of the
hatchlings died within 75 days (Shaw 1954). Death was attributed to
failure of the juveniles to assimilate the yolk mass in the abdominal
cavity. Artificial incubation was attempted on 45 of 50 eggs laid in the
San Diego Zoo by C. cornuta females (Shaw 1969); 6',. hatched and
28.8'( contained dead embryos or young that died within the egg after
having slit the shell with the egg tooth. The percentage of fertile eggs
was not determined. All 20 eggs laid in the Miami Serpentarium by a
C. cornuta hatched (Haast 1969), although two of the hatchlings died
of unknown causes soon afterward.
AGE STRUCTURE.-Iguanas on Anegada (including the Citron Bush,
but excluding Windberg Key) were grouped as juveniles, subadults,
young adults, and older adults on the basis of size and appearance.
These age structures (Fig. 11) are meaningful only for March and April
1968 (5-7 months after presumed hatching). Figure 11 may be confusing
unless one remembers that adults and juveniles did not mix. Thus the
Citron Bush was 100% adults (10% young adults, 90% older adults),
and a cross section of many colonies shows percentages of all age classes.
The age structure of C. pinguis suggests a low annual turnover of

BULLETIN FLORIDA STATE MUSEUM Vol. 19, No. 4

adults. On Anegada adult iguanas comprised over 87 percent of the
population six months after presumed hatching. This suggests that
other than established adults few individuals survive each year. This
contrasts with Uta stansburiana (Tinkle 1967), which exhibits nearly
complete annual turnover, multiple breeding, and early maturation and
live only a year or two, whereas C. pinguis probably attains an advanced
age for a lizard. An experienced "woodsman" on Anegada told me of
several iguanas that had lived on the same retreats since he had been a
child (recognition was based on individual markings). The man was in
his sixties at the time of my research.
Animals in the wild usually die before their potential life span is
attained, often during or before their reproductive prime (Lack 1967),
but island species frequently have fewer competitors and/or predators
than their mainland counterparts. This decrease in competitive inter-
action often results in decreased mortality. Adult C. pinguis on faunisti-
cally impoverished Anegada could realize their potential life span. This
may be true for West Indian rock iguanas in general. A comparison of
Lacerta sicula populations on the Italian mainland (where predators are
numerous) and adjacent islands (where predators are few) (Kramer
1946) showed the average ages for male lizards to be 1.9 years and 4.4
years respectively. Annual adult mortality averaged 40% on the main-
land and 20% on the islands.

older adults
Young adults

o 1 subadults

1 juveniles

I 'I I I I I I I I I
0 10 20 30 40 50 60 70 80 90 100

PERCENT IN AGE CLASS
FIGURE 11.-Age distribution of Cyclura pinguis population on Anegada, British
Virgin Islands, 27 March-5 May 1968. Black bars, all of Anegada; white bars,
Citron Bush.

CAREY: CYCLURA PINGUIS

The population age structure of C. pinguis on Anegada suggests that
juveniles are subject to high mortality before they grow large enough
to fend off predators. Approximately six months after the presumed
hatching period, juveniles and subadults made up only 12.5 percent of
the population, young adults and older adults 87.5 per cent (Fig. 11).
The differential mortality indicated by this disproportionate age structure
suggests decreasing predator pressure on larger lizards. Once large size
has been attained, fewer mortality factors operate. Death of adults ap-
parently results only from hazards during egg-laying, occasional preda-
tion by dogs and man, old age, and environmental catastrophes. Scelo-
porus olivaceus (Blair 1960) and Uta stansburiana (Tinkle 1967) usually
migrate only a few meters from their home ranges to lay, while C.
pinguis females may travel great distances. The greatest mortality of
juveniles probably occurs during the period of occupancy of areas per-
ipheral to the areas occupied by adults. Their small size, coupled with
the relatively recent increase in predators, probably subjects the young
lizards to increased pressure in these areas.

DISCUSSION

A population consisting of a large proportion of old individuals is
frequently thought to be senile or declining, whereas those with a high
proportion of young individuals are regarded as thriving. For example,
in the GalApagos the land iguana, Conolophus subcristatus, is thriving
(large proportion of young) on some islands and declining on others
(only old individuals) (Dowling 1964, Hillaby 1964). No C. pallidus
juveniles were seen on Barrington Island, also suggesting decline, and
land iguanas no longer exist on some islands, such as Baltra and Santiago,
where they were recorded previously. Their extinction on these islands
coincides with the introduction of goats, which are believed to compete
with the lizards (particularly juveniles) for food. Only large adult land
iguanas presently persist on Barrington and Santa Cruz islands, where
goats have been established for some time. Goats feed on vegetation
at the same heights as juvenile iguanas, as well as much higher up than
juveniles can reach, thus easily out-competing them for the vegetative
part of their diet. The goats also clear the area of protective under-
growth, exposing juveniles to predators, especially hawks (Dowling
1964). On goatless Fernandina and South Plaza, land iguanas flourish.
Insufficient evidence is available to predict the future of C. pinguis
on Anegada; but the population seems to be operating at a density level
below that of the past, making extinction a distinct possibility. This con-
clusion is based on: (1) the presence of suitable, but unoccupied habitat;

BULLETIN FLORIDA STATE MUSEUM

(2) the apparent lack of communal nesting that characterizes several
high density iguanine populations, including at least two species of
Cyclura; and (3) the disproportionately high percentage of old indi-
viduals. Similar properties probably were characteristic of the C. collei
populations on Jamaica and its satellite, Goat Island. This species had
been considered extinct on Jamaica since the early 1940's but recent
evidence suggests that at least a few individuals persist in the Hellshire
Hills of southeastern Jamaica (Woodley 1971). On Goat Island, they
definitely are gone. Lewis (1944) saw no juveniles during six months
of intermittent collecting on the island. The 22 animals collected during
that period for transplant to the mainland, definitely were old adults.
The principal factor leading to extinction on Goat Island and almost
total decimation on Jamaica was the mongoose. These animals prey
heavily on juveniles and eggs.
It is probable that ancestral C. pinguis colonized Anegada via Greater
Puerto Rico, from which the former island was separated (became a
discrete land mass) about 8,000 years ago. However, island hopping
remains a possibility (Heatwole and MacKenzie 1967). Osseous re-
mains have been found on Puerto Rico (Barbour 1919) and St. Thomas
(Miller 1918), and were described as C. portoricensis and C. mattea
respectively.
Ancestral C. pinguis were probably herbivorous and entered an en-
vironment essentially free of competitors and predators. The present
decline of the iguana population on Anegada is a phenomenon that may
be attributed to competition and/or predation from an introduced do-
mestic fauna (especially grazing animals), as well as the advanced age
at initial reproduction. West Indian Cyclura occupy feeding niches
roughly equivalent to those of grazing animals elsewhere, as do Galapa-
goan Conolophus (Stebbins 1966).
The reduction in density has created a secondary deleterious situa-
tion, irreversible unless the primary sources of population regression are
eliminated. Removal of females from the Cyclura population is much
more acute in these late-maturing animals. Tinkle et al. (1970) stated
that during the evolution of late-maturing species, these must have been
compensations for fecundity loss. The principal compensation would be
the larger size of the female at maturity, allowing for larger clutch size
and production of larger eggs. The larger body size also might eliminate
some predation, thus increasing adult life expectancy and providing ad-
ditional opportunities for reproduction. In addition, late-maturing lizards
with long life expectancies often exhibit postovipositional parental care,
which should increase juvenile survivorship (Tinkle 1969). Postovi-
positional parental care of the nest has been observed in Cyclura, as well

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CAREY: CYCLURA PINGUIS

as in other tropical iguanines. This and the additional breeding oppor-
tunities through longer life expectancy would defray the reproduction
cost of delayed maturity (Tinkle et al. 1970).
As C. pinguis seems to possess all of the required characteristics for
an intimate evolutionary bond to delayed maturity, any disruption of that
bond could lead to reproductive catastrophe. Cole (1954) emphasized
that population stability in animals with delayed maturity requires the
balance of several factors, such as degree of parental care, clutch size
and frequency, and adult life expectancy. Although fecundity of C.
pinguis probably was sufficient under natural conditions, only a tiny
percentage of offspring currently attain adulthood. If potential produc-
tion (initially reduced for island life via K [carrying capacity] selection)
per adult female is at a physiological maximum for previous conditions
on Anegada, then there are simply not enough reproductive females in
the present population to supply the number of offspring required to
return to the potential value of K. This might be accomplished by any
factor that increases the rate of population growth. Slobodkin (1961)
stated: "physiological properties of each species are intimately related
to its r [intrinsic rate of increase] value and any evolutionary change in r
implies changes in litter size, age at initial reproduction, or longevity, or
some combination of these." He further pointed out that selection for
an increasing r will be expected to result in an earlier onset of initial re-
production in species with small clutches. Cole (1954) stressed the im-
portance of age at initial reproduction, not litter or clutch size, as the
principal factor in population growth.
Delayed maturity in birds such as raptors and swifts is characterized
by single broods per season, high annual adult survivorships, and long
developmental periods (Tinkle et al. 1970), again roughly the conditions
found in Cyclura. An evolutionary increase in r can best be accom-
plished by lowering the age of initial reproduction, thus producing a
substantial increase in offspring per female-lifetime. An increase in off-
spring might assure an ultimate return to K.
The discussion of population decimation in C. pinguis probably can
be applied to the recent extinction or depletion of C. collei on Jamaica
and Goat Island and C. nigerrima on Navassa. The Jamaican popula-
tions consisted only of a few very old adults (Lewis 1944). There sim-
ply were not enough females, even if they did reproduce, to overcome
the tremendous pressure against the juveniles.
The circumstances surrounding the apparent extinction of C. niger-
rima on Navassa are unknown. The five specimens in museum collec-
tions were taken in the late 1800's. Neither Thomas (1966) nor Patton
(1967) saw living iguanas during their brief visits to Navassa, although

BULLETIN FLORIDA STATE MUSEUM

the latter reported finding fossil material. Thomas stated that the island
presently is uninhabited, but previously was occupied by the Navassa
Phosphate Company (1864 to 1898), by three families of lighthouse
keepers (1917 to 1929), and by the U.S. military during World Wars I
and II. As a result of these human agencies, Navassa now has an intro-
duced fauna of rats, cats, and goats-seemingly major offenders in the
decimation of land iguana populations.
The Grand Cayman population, C. macleayi lewisi, currently is
meager, although the causes are unclear. Grant (1940b) thought that
the population consisted of about a dozen individuals; the animals were
so scarce that many of the natives were unaware that iguanas even
existed on Grand Cayman! It recently has come to my attention (Wayne
King, pers. comm.) that within the past few years a pair of young C.
macleayi caymanensis from Little Cayman were released on Grand Cay-
man. This is indeed alarming since these animals apparently have sur-
vived and reproduced, thus threatening through competition and/or in-
tergradation the already highly precarious existence of C. macleayi lewisi.
Dr. King has informed me that action will be initiated to remove these
alien iguanas from Grand Cayman as soon as possible.

CONSERVATION

At this writing, the Caribbean Research Institute of the College of
the Virgin Islands is attempting to save C. pinguis. This project is being
funded by the New York Zoological Society and the World Wildlife
Fund. Unfortunately, recent efforts to breed the species in large en-
closures have failed (Edward Towle, pers. comm.). The ideal solution
would be the removal of all domestic animals from Anegada. However,
since livestock is an integral component of the food supply of the native
population of Anegada, attempts to eliminate these animals undoubtedly
would meet insurmountable opposition.
Whatever the methods, steps must be taken now to ensure the con-
tinued existence of C. pinguis on Anegada. In fact, a general statement
to this effect should be made in regard to the entire genus. Although
many species actually are not endangered presently, all are listed as de-
pleted in the IUCN's RED DATA BOOK on endangered amphibians
and reptiles (Honegger 1968). They occupy such restricted or special-
ized habitats that little environmental disruption would be required to
dangerously upset the populations.
The allocation of setting aside iguana preserves with resident wardens
as advocated by the IUCN is only part of the answer. I feel that a more

Vol. 19, No. 4

CAREY: CYCLURA PINGUIS

productive solution would be the education of the native islanders about
the importance of their own natural fauna. If the steady and devastating
advances of tourism cannot be halted, then extensive national parks or
preserves (both desirable to, and usually respected by, tourists) should
be set aside wherever Cyclura species occur. Iguanas, though repulsive
in appearance to many, are still great curiosities to the general public.
This could be coupled with rigid protection measures enforced by the
natives.
On human-inhabited islands, livestock should be excluded from the
preserves, not necessarily from the entire island. On small uninhabited
islands (such as in the Bahamas) there is no domestic livestock. Here
collecting and needless slaughter for "sport" provide potential danger.
All collecting should be deemed illegal, unless for breeding purposes in
approved zoos or similar scientific institutions. Success in breeding
Cyclura under proper captive conditions is becoming well known (Shaw
1954, 1969, Haast 1969, Murphy 1969, Burchfield 1973). Breeding pro-
grams in zoos could perform dual functions: (1) for trading purposes
with other zoos, thus relaxing collecting pressure on natural populations;
and (2) for recycling fit juveniles back into natural populations after
principal decimating factors have been removed. Employment of the
latter function has been successful in the Galapagos Islands with several
races of the Galapagos tortoise, Geochelone elephantopus (Perry 1970,
Pritchard 1971).
I believe that this program would enhance greatly the survival
chances of the Cyclura population on Anegada, at least, and possibly
wherever other populations exist. Also, wherever such programs are in
operation, comprehensive surveillance at regular intervals should be
maintained on the populations. Further investigation of the status of
all other Cyclura populations (especially on human-inhabited islands)
is needed to determine the applicability of protective measures similar
to those outlined above. At this writing, a Cornell University graduate
student, Thomas A. Wiewandt, had just begun an ethoecological study
of C. stejnegeri on Isla Mona.

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